The present invention relates to a linear moving type carriage assembly for use in disk drives and, more particularly, to a magnetic head support mechanism for supporting upper and lower magnetic heads that write/read data on a magnetic disk medium in a flexible disk. As is well known in the art, disk drives are a type of a magnetic data recording/reproducing device on which a flexible disk can be mounted for the purpose of recording and reproducing data. Flexible disks have recently been increased in storage capacity. Typical flexible disks have a normal storage capacity between 1 and 2 megabytes. There flexible disks with a storage capacity of 128 megabytes have recently been developed. Such flexible disks are referred hereinafter to as flexible disks of the large capacity. In response to such a trend, disk drives have also been developed that can be used with the flexible disk of the large capacity.
The disk drives used With a flexible disk of the normal capacity have different mechanisms from those of the large capacity. One of the differences lies in the structure of driving unit for use in driving a carriage adapted to support a magnetic head in a manner to allow swing thereof. The carriage is for use in moving the magnetic head in a predetermined radial direction relative to the flexible disk mounted within the disk drive. The disk drive for the normal-capacity flexible disk uses a stepping motor as the driving unit. On the other hand, the disk drive for the large-capacity flexible disk uses as the driving unit a linear motor that is called a voice coil motor.
The voice coil motor is mounted on a rear portion of a carriage assembly. The voice coil motor comprises a voice coil and a magnetic circuit. The voice coils are wound around a drive shaft that is arranged in parallel with the predetermined radial direction. The magnetic circuit is used in generating a magnetic field in a direction intersecting that of electric current flowing through the voice coil. With this configuration, the interaction between the electric current and the magnetic field produces a driving force on the voice coil in the extending direction of the drive shaft when the electric current flows through the voice coil in the direction intersecting that of the magnetic field generated by the magnetic circuit. The voice coil motor can thus move the carriage assembly with the driving force in the predetermined radial direction.
As is known in the art, the flexible disks include a cover consisting of an upper cover section and a lower cover section, and a magnetic disk medium contained in the cover. Upper and lower access slots are formed in the upper and the lower cover sections, respectively, at a corresponding location. The magnetic disk medium is accessed by upper and lower magnetic heads through the upper ad the lower access slots, respectively. The surface of the magnetic disk medium is divided into a number of concentric circles. Each concentric circle is called a track and is used to store the data. The tracks on the large capacity flexible disk are smaller in width than those of the normal capacity.
The magnetic disk medium in the flexible disk of the normal capacity is rotated typically at a rotation speed of 300 rpm while the one of the large capacity is rotated at 3,600 rpm. The magnetic disk medium rotates at a high speed in the flexible disk of the large capacity. It is thus necessary to avoid direct contact between the upper and the lower magnetic heads and the magnetic disk medium while writing and reading data. For example, the flexible disk of the large capacity requires a gap of approximately several ten nanometers between the upper and the lower magnetic heads and the magnetic disk medium. The magnetic disk medium in the flexible disk of the large capacity is moved upward and downward like wave when it is rotated at a high speed, because of flexibility of the magnetic recording medium itself.
As is well known in the art, in hard disk drives, the magnetic disk medium is incorporated in the magnetic recording/reproducing device. The magnetic head is supported by a support spring that is called a load arm. The magnetic head comprises a core and a slider. The core is for use in recording data on the magnetic disk medium. The slider is for floating the core over the surface of the magnetic disk medium with a small gap called spacing. The magnetic head of the type described is called a monolithic head. It is not assumed for the hard disk drive that the magnetic disk medium is moved upward and downward during rotation. In the case that the above-mentioned support mechanism is used for the magnetic head, the magnetic head is displaced out of a predetermined track position over the magnetic disk medium when the magnetic disk medium is flexible like the one in the flexible disk.
Taking the above into consideration, the applicant of the present invention has proposed a linear moving type carriage assembly for flexible disk drives" in Japanese Patent Laid Open No. Tokkai Hei 9-312055 (312055/1997). This carriage assembly is described with reference to FIG. 1.
In FIG. 1, a flexible disk 1 mounted on a flexible disk drive is depicted by a dot-dash line. The flexible disk 1 comprises a case with an upper case member 1-1 and a lower case member 1-2, and a magnetic disk medium 1-3 contained in the case. An upper magnetic head 11 is for recording and reproducing data through an upper access slot in the upper case ember 1-1. The upper magnetic head 11 is supported on an upper carriage 12 at an end thereof. A lower magnetic head 13 is for recording and reproducing data through a lower access slot in the lower case member 1-2. The lower magnetic head 13 is supported on a lower carriage 14 at an end thereof. Strictly speaking, the upper carriage 12 comprises an upper pivot 12-1 and an upper gimbal plate 15 at an end thereof. The upper magnetic head 11 is held by the upper gimbal plate 15 about the upper pivot 12-1 to allow swing of the upper magnetic head 11. Likewise, the lower carriage 14 comprises a lower pivot 14-1 and a lower gimbal plate 16 at an end thereof. The lower magnetic head 13 is held by the lower gimbal plate 16 about the lower pivot 14-1 to allow swing of the lower magnetic head 13. A bias spring (head load spring) 17 applies a predetermined downward urging force to the upper magnetic head 11.
With this structure, the upper and the lower magnetic heads 11 and 13 swing about the upper and the lower pivots 12-1 and 14-1, respectively, even when the magnetic disk medium 1-3 floats up and down This makes the upper and the lower magnetic heads 11 and 13 follow the wavy movement of the magnetic disk medium 1-3. For a flexible disk of a large capacity, a predetermined gap can be kept between the upper and the lower magnetic heads 11 and 13 and the magnetic disk medium 1-3 while rotating at a high speed. The upper and the lower magnetic heads 11 and 13 are held at a predetermined track position over the magnetic disk medium 1-3 even with the up-and-down movement of the magnetic disk medium 1-3 during rotation.
However, the following problems arise because the upper carriage 12 is attached to the lower carriage 14 through the head load spring 17. An external force such as vibration and shock tends to vibrate the upper magnetic head 11 with the substantially no movement of the lower magnetic head 13. As a result, opposing relation is not stable between the surface of the magnetic disk medium 1-3 and the head face of at least one of the upper and the lower magnetic heads 11 and 13. Such an unstable opposing relation makes it difficult to improve the accuracy of the magnetic head output.